Type B intercalated cells are expressed within the cortical collecting duct (CCD) and the connecting tubule (CNT), where they act to secrete HCO3- and absorb Cl- across the apical plasma membrane, through the Cl-/HCO3- exchanger, pendrin. Pendrin-mediated HCO3- secretion reduces arterial pH and HCO3- concentration, which contributes to the correction of a metabolic alkalosis. Moreover, pendrin-mediated Cl- absorption augments vascular volume, which raises blood pressure. Since pendrin is regulated by aldosterone and angiotensin II and since many of the effects of aldosterone and angiotensin II are mediated by changes in nitric oxide availability, we will test the hypothesis that nitric oxide (NO) modulates pendrin abundance and function through cyclic nucleotide-dependent pathways. Published and preliminary data show that nitric oxide reduces HCO3- secretion and Cl- absorption within the CCD, which most likely occurs in part by inhibiting pendrin-mediated Cl-/HCO3- exchange. Our preliminary data show that with longer-term exposure to the nitric oxide synthase inhibitor, L-NAME, pendrin abundance increases both in vivo and in vitro. These data support the hypothesis that NO modulates pendrin abundance and function. We hypothesize that nitric oxide acts on pendrin abundance and function primarily by reducing cAMP availability. The purpose of this proposal is to characterize the effect of nitric oxide on Cl- absorption and HCO3- secretion in the CCD and to determine the transport mechanism and the signaling pathway by which this occurs. We will also examine the mechanism by which nitric oxide regulates pendrin abundance in vivo and in vitro. These studies will elucidate how Cl- absorption is regulated in the CCD and the CNT and thus how these segments modulate blood pressure. The proposal's specific aims are the following: Aim 1: To determine the transport mechanism by which nitric oxide modulates anion transport in mouse CCD in vitro. Aim 2: To determine the signaling mechanism through which NO modulates anion transport in vitro in mouse CCD. Aim 3: To determine how NO modulates pendrin protein abundance in vitro and in vivo. To accomplish these objectives, the regulation of pendrin abundance and function by NO and the signaling mechanism by which this occurs will be examined in tissue from wild type and genetically modified mice both in vivo and in vitro using using quantitative real time PCR, light microscopic immunohistochemistry, immunogold cytochemistry, immunofluorescence and immunoblots. Transport studies will be performed in renal tubules perfused in vitro.